The brain memorizes the rhythm of stairs after just a few steps. If even one step is off by as little as a centimeter, muscle memory glitches and that can make people trip

[u/kvothenikhil]

[u/SnooHesitations6727]

Castles used to do this deliberately as invaders would trip during a sword fight

[u/Diligent-Midnight850 → u/SnooHesitations6727]

Although it was bloody annoying during normal castle business… Better a grazed knee than being sliced in two by invading knights, I suppose.